Lc type transistor oscillator



Jan. 2, 1962 E. B. VASS 3,015,785

LC TYPE TRANSISTOR OSCILLATOR Filed Dec. 29, 1958 4 Sheets-Sheet 1 -9Volts FFN'N'M all SYNCRON \ZHJG SIGNAk 'SOURQE.

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Aczoss LC \A/AVEFORM AT COLLECTOR OF T WAVEFORM AT COLLECTOR OF '2 FIG. 2

INVENTOR ERIC BURNETT VA 5 3 A NT Jan. 2, 1.962 E. B'. was 3,015,785

. LC TYPE TRANSISTOR OSCILLATOR Filed Dec. 29, 1958 4 Sheets-Sheet 3 FoQM AT COLLECTOR OF T. THOUT 5\/NCHQON\Z.AT\ON WAVEF'ORM AT COLLECTO2 oFTz wrruou-r syncuzowvzprrwnl 4 Q INVENTOR ERIC BURNETT VASS BY MAL-f A NT United SW65 This invention has for its principal object to devise a circuit for an oscillation generator tions of a stabletfrlequencyiwhich may be synchronizedfby the injection of h'ig'horder harmonicsof the' fr'equency to be generated and/gr' which may bejused for the producf ion of highharmonics of the frequency of theloscillations generated bythe'circuit. a

One of the 'main'jrequirements of anjoscillator such for producing oscil-la-.

atent .as that enyisaged by this invention is that it should 'possess an inhetent frequency stability in order to: minimize of the'synchronizing' frequency,

Anoscillator circuit the possibility of locking Ito an'jundesired' s ub-harmo'nic w r n 't e lren s is P imarily stabilized by means pfan inductance capacitance I tuned-to approximate resonance with the desired frequency to be generated. p v I One terminalof this inductance'is connected to a point of constant potential and the other terminal to' the'base electrode of a first transistor;

this first transistoris the base of the transistor, theerhitter Of' hi transistor is similarly fe'dviaa resistance from a of conr'l'fhef collector electrodebf j fed througha' resistance from a point of constant potential which'is negativewith' respect-to stant potential which is positive with respect to "the'ba'se l of" the transistor. V, I 1 e H The emitter of this first transistor is also connectedto the emitter of a second transistor, the baseeleetrode'of which is connected to the point of constant potential to which one endof the said inductance is connected; The

collector-of this second'transisto'r is connected via a suit able resistance to a point of constant potentialnegative with respect to the base and'is also coupledto the emitter of a third transistor by means ofa coupling capacitor or other suitable means.-

a 1 Moreover, the emitter of thisthird transistor is'connected via a suitable'resistance to a point of constant potential which is also connected to the base of this third transistor and which is positive with respect to the potential of theend of the inductance connected to a pointofconstant potential. a I

The collector of this third transistor is connected to the base of'the first transistor which, as has been stated above,

is connected to one end of the said inductance.

This circuit forms an oscillation generator of marked I inherent frequency stability. In one embodiment of the invention a change inany component value other than those forming theresonant circuit of plus or minus 20 per- 'cent caused a change in frequency of less than 0.3 percent. Simultaneous changes of up to 50 percent in the positive and negative potentials feeding the transistors have a negligible eflect on frequency, while a reduction of the total supply voltage from 18 volts (9 volts plus +9 volts) to six .volts (-3-Volts plus +3 volts) varied the frequency of:the 'oscillations'generated' by only 0.4 percent. The output of this oscillation generator circuit with a total supply voltage of 18 voltsproduced a'g'ood sine wave of 2.5 volts R.M.S. across'the inductance with a total current drain of only 0.2 milliampere. i

High order harmonics may be conveniently derived from the collectors of the first or second transistors,

;Th is circuit has been vfound to be particularly suitable for synchronization by means of a frequency which is a vhigh harmonic of the frequency olfrthe oscillations to be circ1 1itsusceptible to synchronization which can 'w leafhrecision.

the Wave as a I picted in FIG. -1 of the accompanying drawings.

3,015,785 Patented Jan. 2, 1 962 2 r, either in series with the base'of the second transistor or in series with theresistor which is common to the emitters of the fi'rstand second transistors; In the embodiment referred to above synchronizatiofwas achieved success fully with-frequencies as high 'as 200 times the frequency which it isgdesired to generate.

These various advantages are very high'irnpedance of the collectorjo'f the third transis torlwhich enables thiselectr'ode'to be connected directly to the tuned circuit, and-tofthe' combination of the short base of the 'trans'istors and -high'loop gain which produces a wave form having a very steep front thus rendering the be of The invention thus primarily consistsin an oscillation 'g'eneratorfwhich comprises a' tunedor resonant circuit in combination 'with means for deriving from-the oscillations generatedin the tuned. circuit a wave (if substantially rectangular wave form; and "means for amplifying the said substantially rectangular wave in combination with means for feeding back the amplified substantially rectangular wave in the proper phase to maintain- 'the oscillations in the tuned circuit. i

Such an oscillation generator may be stabilized, according to-the invention, bysuperimposing a wave of suitab le frequency either on the generated wave be fore' deriving the substantially rectangular wave; or upon the substantially rectangular wave after it has been'derived but be tore it is fed back to maintain oscillationsIfIf the synchronizingwave is' superimposed on the wave; of substantially rectangular waveform, it-may be superimposed on whole, or only or mainly upon positive or neg 'tive excursions of: the wave and on the sloping sides of the substantiallyrectangular Waveform. J

quency divider delivermg to an output circuit a wave having a freque'ncy which is a" small fraction of thei f r'e'quen'cy of the synchronizing wave or in certain'cases' a multipleof such a fraction. g 3 H A circuit? according "to: the invention whichj generates oscillations of reasonably good frequency stability is de- In EIG.;1 ,L denotes a'n inductance tuned "to the desired frequency by a shuntcondenser C. One terminal of the inductance is connected, preferably via' a ground connection, to the centre tap 2 of an 18 volt battery or other source 1 o f=.D.C. power, while the'other terminal of the inductance is connected to the base electrode B of atransistor T The collector C of this transistor is connected to the negative terminal 3 of the power source 1 via a resistance R of about 22,000 ohms, while .the emitter E of the same transistor Ti'is connected to the positive pole of the power source 1 via a resistance generated. Such a'synchronizingsignal may be injected to the negati R1 of about 47,000 ohms and also to the emitter electrode E of a second transistor T The collector C of this second transistor is connected ve terminal 3 of the power source 1' via a resistance R3 of-about 22,000 ohms, While the base B of this second transistor is connected to the "centre tap 2 of the power source 1,'for instance viaa ground connection; 1

The collector electrode C of-t'ransistor T is also connectedvia a blocking condenser C to the emitter electrode'E of a third transistor T the base electrode B of which is connected to the positiveipole 4 of the power source 1 and -the collector electrode C of which is connected to a tap on the tuned circuit.

The translstors are of-gthe type known as OC73. Theoperation of this'circuit when generating scillations may be explained as'follows. I

If it be assumed that'oscillations exist in' the tuned cirbelieved to be due to the I 3 cuit formed by the inductance L and the capacity C, these oscillations will apply to the base electrode B of the transistor T an oscillating voltage. The electrodes of the transistor T are so biased by the power supply source 1 and the resistances R and R that the collector current of the transistor T is greatly reduced when the transistor T is passing collector-current, and vice versa, under which circumstances practically only negative half cycles of the oscillatory voltages will pass through the base emitter circuit of the transistor T which in effect will clip the positive half cycles of the sinusoidal wave.

These negative half cycleswill cause a positive going part of a cycle of current. of approximately rectangular waveform to flowthrough the collector emitter pathof he t ans t 1- As the emitter E goflithe transistor T is connected to the emitter electrode E of transistor T the voltage of the emitter of this transistor T will vary similarly to that ofthe emitter T thuscausing substantially rec' tangular half cycles of current to flow through the collector electrode of the transistor T having a phase similar to that ofthe half cycles of current through thecollector C but v'vith clipping of the negative half cycles. These half cycles of voltage will he transferred to the emitter el s d 3 f e-th r ns r T3 by h bl c condenser C I r 7 The connections of this transistor are. such that negligible current flows from the power source 1 unless the emitter electrode E5 has its; voltage with respectto' the baseelectrode B increasedin a positive direction. When this occurs, pulses of current will flow through its collector. electrode C via the inductance L, the direction of these pulses being such as to tend to maintainoscillations in the tuned circuit formed by inductance L and q tvv It will be noted thattheonlydamping. effective in the tuned circuit L, C; apart fromtitsown resistance, is the in FIG. 3. In this figure curve (a) is the waveform at the emitter electrodes or the transistors T and T with the sychronizing wave switched off, While curve (b) is the waveform at the same point with the synchronization wave switched on. It will be seen that the positive going half cycles of the combined wave are clipped whereas the negative going half. cycles are not clipped.

Curve (0) in FIG. 3 shows the waveform at the collector electrode of the transistor. T with the synchronizing wave switched"oir"-,-while curve (d) in the same figure shows the waveform at the same point with the synchronizing wave switched on. It will be noted that at collector electrode the negative going cycles of the.

waveform are very severely clipped. 1 Curves e and (f): of FIG. '3 show the waveforms at the collector electrode of the transistor T curve (e) being that with, the synchronizingwave switched off and a curve (f) being that with the synchronizing wave switched on. It willbe noted that the positive going half cycles are very severely clipped, whereas the clipping on the negative. cycles'is not so severe, Furthermore it will be seen that the synchronizing wave is very much in evidence on the steep sides of the substantially rectangular waveform. Ithas been observed that synchronization occurs while these pulses. from the synchronizing wave remain on-the slopin'g'sides, but, when thepulses move so that they fall on the fiat top of the rectangular curve (I) or .z if the amplitude of the synchronizing-waveis increased so that his. comparable with that of the substantially rectangular waveform, the synchronization slips.

The waveform of curv'etf) of FIG. 3 forms thebasis of thefpulses. applied to the tuned circuit L, C by the resistance of-rthe base electrode of transistor T and of the collector of. transistor T and, as theresistance of the transistors viewed fromthese electrodes is veryhigh, the damping due to these electrodes is very small andconse quently the frequency stability ofi-the oscillations is very It will. be seen from FIG. 2 d)-that the wave at the collector electrode of transistor T is substantially rectangularin shape.

The amplitude scale of curves (c) and (d) is ap.- proximately one-tenth of that of curves (a) and (b), there. being appreciable voltage amplification in the transistors.

As the collector electrode. of the transistor T is coupled to the emitter electrode of the transistor T the collector of which is coupled to the tuned circuit L, C, pulses of-the waveform shown in curve (d) will be applied to the said tuned circuit. 'I'husthe circuit in effect amplifies and clips the sinusoidal wave generated in' the tuned circuit .to produce a wave of substantially rectangular waveform which is fed back to the tuned circuits for producing oscillations.

The circuit depicted in FIG. 1 has been found to be particularly susceptible'to synchronization by a wave of much higher frequencywhich maybe applied to any convenient point in the circuit. Examples of waveforms which occur when: such a synchronizing wave is applied in series with the tuned circuit'L, C and the base electrode of transistor T the synchronizing wave being superimtransistor. T with the possibility that the pulses will be still further. clipped in. that transistor. 'As .the tuned circuit L, C'is not resonant with the synchronizing. wave,

presumably only the substantially rectangular, pulses will tend. to maintainoscillations, this presumption being mentioned to add clarity to a possible explanation of the synchronizing process given later. I

Thewaveforms shownin FIG. 4 are those at various points of. the circuit when the synchronizing wave applied in series with the base electrode of transistor. T Curves '(a), (b-) (d) and (f) are forthe waveforms at the base clectrodeof the transistor .T at the emitter electrode of transistor T the collector electrode of tran sistor T and at the collector electrode of transistor T respectively, without the synchronizing wave switched on these being similar to the waveforms of FIG. 2.

Curve (0) of FIG. 4 shows the waveform at the emitter electrodes, of the transistors T and T with the synchronizing wave applied to the base electrode of transistor T andit will be observed that the negative going half cycles are severlyclipped, the synchronizing wave appearing only on the fiattops of the substantially rectangular waveform.

Curve (e) of the same figure shows the waveform at the collector electrode of the transistor T and it will be noted that the negative going half cycles are severely clipped, the positive going cycles are partially clipped and the synchronizing waveform is substantially in evidence only on the sloping sides of the substantially rectangular Waveform.

Curve (g) of FIG. 4 depicts the Waveform at the collector electrode of the transistor T and it will be observed that the synchronizing waveform is mainly in evidence on the sloping sides of the substantially rectangular waveform, is only slightly in evidence on the negative going half waves of the Waveform, and is not in evidence at all on the top of the positive going half cycles. This waveform closely resembles that of FIG. 3( with more perfect clipping of the positive half cycles.

This waveform shown in FIG. 4(g) is thebasis of the waveform of the pulses applied to the tuned circuit L, C

comprise the substantially rectangular waveform with the high multiples of the frequency of the generated oscillation! "Observationshows'thatfthis resistance affects the steepness and hence the duration of the steep sides-pf the substantially'rectangular waveform.- Y i has also bee rmnia that the'co'nnection of a'r e'ctifier D acrossthe resistaneeR; (asshown-indotted lines) in FIG. ilfw'i h its directionofcondiictivitythereverse to tions, but that such synchronization was also .secured by synchronizing waves which were a high multiple of a fraction of the frequency of the generated oscillations, the

two frequencies being related only in that they had a ;l

common factor.

The curves (a), (b) and (c) in FIG. depict waveforms at the collectorelectro'de of transistor T for cases in which the synchronizing wave had a frequency whichwas a multiple respectively of one half, one third and one fifth of the frequency of the generated wave.

that the emitter; still further improves the (facility of the circuit to accept synchronization. Such: a: rectifier preventsthe' accumulation of anelect calchargebetween the emitter and itscurrcnt supply arid also possibly improves the clipping action of the circuit and it assists in obtaining a substantially rectangular waveform with the synchronizing wave mainly confined to its steep sloping It will be observed that successive cycles of these wave;

forms are dissimilar, but that the waveforms of the cycles are repeated at intervals depending upon the highest common factor of the two frequencies. It will further be seen that either one cycle of the synchronizing wave is present on the sloping sides of thesubstantially rectangular waveform or none at all. Nocase was observed in which synchronization occurred and in which more than one cycle of the synchronizing wave was present on the sloping sides of the rectangular wave although it may very well be that such could occur with extremely high frequency synchronizing waves. These matters are mentioned in order to add clarity to the possible explanation of the functioning of the invention given later. If the synchronizing wave is superimposed, ,at theemitter electrodes of the transistors T and T on the substantially rectangular waveform of the wave derived from the generated oscillati0ns, the waveform at the collector electrode of the transistor T is of the form shown in FIG. 4 but inverted,

the synchronizing wave appearing mainly on the sloping sides of the substantially rectangular wave and in clipped form on the flat top of the positive half cycles of the substantially rectangular waveform, practically none being apparent on the negative half cycles.

It is thought that the remarkable facility with which oscillations generated in circuits according to the invention can be synchronized, is probably due to the fact that the superimposed synchronizing wave is in evidence exclusively or mainly on the steep sloping sides of the substantially rectangular waveform and that, in addition to there being some numerical relationship between thefre quencies of the synchronizing wave and of the generated oscillations, there might be someapproximate relationship between the duration of the said steep sloping sides and the duration of one cycle of the synchronizing waves. This results in a modification of the frequency of the generated wave such that the energy content of the effective portion of the substantially rectangular pulses fed back to maintain oscillations remains constant with the synchronizing wave superimposed on these steep sloping sides despite any dissimilarity between the shapes of the successive individual substantially rectangular pulses, this action differing somewhat from the action of a synchronized sinusoidal valve oscillator in which short pulses superimposed on the sinusoidal waves result in an earlier commencement of the feeding back of energy from anode circuit to maintain oscillations in the tuned circuit of the well-known oscillating valve circuits.

It has been observed that if a variable resistance (not shown) be connected between the tuned circuit L, C in FIG. 1 and the base electrode of transistor T adjustment of this variable resistance can bring the tuned circuit into a condition suitable for synchronization, provided that the tuning of the tuned circuit is substantially correct. The ease with which this can be done suggests, that some effect other than the slight change in resonance frequency of the tuned circuit caused by variation of this resistance assists in promoting a condition suitable for synchronizasides for feed-back purposes. 5 7 I Moreover it has been observed that, if the amplitude of the synchronizing wave is made so great that it is not removed from the tops. and bottoms of the substantially rectangular waveform by the clipping action, the facility of the circuit to accept synchronization is very materially reduced, synchronization no longer being possible by a wave having a frequency which is very high in comparison with the frequency of the generated oscillations.

The output of an oscillation generator having the circuit shown in FIG. 1 may be taken from many points in the circuit but, according to the invention, the output should preferably be derived from the collector electrode of the transistor T Shunt alternating current loading at this point has very little effect upon the functioning of the circuit; The waveform at the collector electrode of transistor T has a substantially rectangular waveform component which maybe easily isolated from the other components present and, consequently, it is particularly usefulwhere an output of rectangular waveform is desired. On theother hand, a substantially sinusoidal waveform can be derived from the tuned circuit L, C by known cuit,. first, second and third transistors each having abase,.emitter and collector electrode, a source of voltage having first and second terminals and an intermediate terminal, means connecting the base of said first transistor to said; intermediate terminal by way of said resonant circuit, common resistance meansconnecting the emitters of said first and second transistors to said first terminal,

separate resistance means connecting the collectors of said first and second transistors to said secondterminal, means connecting the base of said secondtransistor to said intermediate terminal, means connecting the base of said third transistor to said first terminal, means connecting the collector of said third transistor to the base of said firsttransistor, resistance means connecting the emitter of said third transistor to said first terminal, and means coupling the collector of said second transistor to the emitter of said third transistor.

2. An oscillation generator comprising a resonant circuit, means for deriving from said resonant circuit a wave of substantially rectangular waveform, and means for feeding back said wave to maintain oscillations in said resonant circuit, said means deriving a rectangular wave comprising first, second and third transistors each having a base, emitter, and collector electrode, a source of voltage having first and second terminals, common resistance means connecting the emitters of said first and second transistors to said first terminal, separate resistor means connecting the collectors of said first and second transistors to said second terminal, capacitor means coupling the collector of said second transistor to the emitter of said third transistor, resistor means connecting the emitter of said third transistor to said first terminal, means connecting the base ofsaid third transistor to said first terminal, one end of said resonant circuit being connected to the base of said first transistor, the other end of said resonant circuit and the base of said second transistor being connected to a tap on said source, said feedback means Referegces Cited in the fiieof this patent UNITEDSTATES PATENTS. 2,794,124 Pgripgton May 28,1957

- OTHER REFERENCES TPortabl e Transistcr Frequezicy stgljdard, b3 Beyer Qin Electronics-pages; 194, 196,;June 1957. 

